In conventional shower stall construction the entrance threshold is elevated above the floor of the shower to prevent the escape of water. In the construction of custom, tile-lined shower stalls it is the usual practice to set up a form of the general configuration of the threshold and pour mortar into the form to provide a base for the threshold. When the mortar hardens, usually within 24 hours, the form is removed and ceramic tile is adhered to the top and side faces of the formed mortar base. This is a time consuming and expensive procedure because the crew fabricating the stall must make two trips to the construction site, one to build the form and pour the mortar, and another, after the mortar hardens, to remove the form and apply the tile. A threshold formed in this manner is illustrated in U.S. Pat. No. 2,005,173 granted Sept. 22, 1936 to H. S. Deubelbeiss for "Bath Tub".
It has been proposed that the inner portion, or base, of the threshold be formed of precast concrete which can be carried to the construction site. Such items are heavy and unwieldy and particularly difficult to use if the length of the threshold does not match the length of the precast section. Cutting precast concrete requires special tools and is time consuming. It has also been proposed to make precast sections from lighter weight materials, such as foamed plastic, but sections made from these materials are fragile and do not constitute a reliable base for the threshold which often is subjected to the weight of a person entering and leaving the shower stall.
Another approach to shower stall threshold fabrication is suggested by U.S. Pat. No. 2,757,385 granted Aug. 7, 1956 to W. W. Whittick for "Shower Receptor", which discloses a "shower receptor", or floor pan, of fiberglass reinforced plastic material and having a threshold formed integrally therewith. For reasons of economy such structures usually can be made only in a limited range of sizes and shapes so they do not lend themselves to custom installations calling for different sizes and shapes of shower stalls.
Now it has been suggested that building wall structures can be fabricated by pouring concrete bonding material between spaced concrete facing blocks which become locked in place when the bonding material hardens. U.S. Pat. No. 1,071,467 granted Aug. 26, 1913 to R. T. Savage for "Building Construction" discloses such a technique, but contains no suggestion that it might be applicable to shower stall structures.
There remains a need, therefore, for a shower stall threshold structure which can be quickly and inexpensively fabricated and which will possess sufficient strength and integrity to last the life of the building in which it is installed.